Internal grinding machine



Sejat. 30, 1952 M. L. KUNIHOLM ETAL 2,612,003

" INTERNAL GRINDING MACHINE Filed April 10, 1951 5 Sheets- Sheet 1 a QED. 1'

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I INTERNAL GRINDING MACHINE Filed April 10, 1951 5 Sheets-Sheet 2 53 I hl 6f k 40 4.1 63 e1 50 48 55 i3 1 martin Leonard Kuhiholm v Tohn. Klqf sa 9MQ+JM wi maln P 1952 M. KUNIHOLM EI'AL 2,612,008

INTERNAL GRINDING MACHINE Filed April 10, 1951 5 Sheets-Sheet a mar'fin Leonafcl Kumholm John Klar Sept. 30, 1952 M. 1 KUNIHOLM ETAL 5 ,008

INTERNAL GRINDING MACHINE Filed April 10, 1951 s Sheets-Sheet 4 as Q 1 5-. 0 III, 0 r f 193 Q 193 400 14-0 .170 .180 FRONT VALVE REAR, FEED VALVE. POWERREVERS'SWIVELSWIVEL ONSET VALVE VALVE ING ONSET OFFSET VALVE VALVE VALVE VA LVE 101 203 20411 10911. Z091: 121 209C 21011131 201E ZOBZMe Z01 14120411 151 161 E11 171 2031181 Z0311 1m LEPCPRCPR-CCCERPOUTRPLELE ZTMVR51N111111111111111-1N111111 :3RAPIDINFEED11111CQPEL,P11C110$ LE 1 1 RT fl' nouerl111111111CP11LC1111111 5:: 1I "I RPCPCLC1(licfiiv11 1 111T1P el flfi g 111111111111111-111111 11 7FINI5H LEPCP111111P111111LE1T 8:531:33 11 1R1PR1 1cE11ouT1 1 11 11 9?,.""11 1 1 1 1 1 1 11 1 1 1RP 1'RP1 1LE l LEFT P =FRESSURE E= EXHUST Ce.= CENTER C= C L05 ED 0s= OSCILLATE POSITION OF FIGS. 1 ANIID a 31W 1 1111111111 Leonard Kumholm John Mar @9541 9 1* Sept. 1952 M. L. KUNII-IOLM ETA L 2,612,008

INTERNAL GRINDING MACHINE Filed April 10, 1951 5' Sheets-Sheet 5 marfin Leonard Kunih 01m v John Klcw f /JW Patented Sept. 30, 1952 2,612,008 INTERNAL GRINDING MACHINE Martin L. Kuniholm, Worcester, and John Klar, West Boylston, Mass., assignors to The Heald Machine Company, Worcester, Mass, a corporation of Massachusetts Application April 10, 1951, Serial No. 220,296

19 Claims. 1

This invention relates to internal grinding machines and has for its general object to increase the speed and accuracy of the precision grinding of the internal surfaces of revolution of work pieces.

In the usual internal grinding machines, a wheel head and a work head including a work carrier structure which revolves the work are so arranged that one may be traversed with respect to the other so that the wheel and the work can be brought together into an operative position with the wheel inside the work piece, and also so that the wheel may be fed crosswise relative to the work to move the wheel against the work surface in order to grind it. Such machines are also provided with a dressing or truing tool which trues the surface of the wheel either during the grinding cycle or thereafter. In the rest or loading position of such a machine, the wheel head and the Work carrier are separated so that the work carrier may be loaded, When the cycle is started, the work carrier or the wheel head traverse in" to bring the wheel and work into relative operative position, and this is accomplished by mounting either the work carrier or the wheel on a longitudinally slidable traverse table. Then the wheel is moved crosswise relative to the work in a direction normal to the axes of revolution of the wheel and work in a rapid infeed step in order to bring the wheel surface into approximate contact with the work surface. Such relative crossfeed of the wheel relative to the work is accomplished by mounting either the work carrier or the wheel head on a crossfeed table which is slidable in a crossfeed direction.

Just as a wheel makes contact with the work, or preferably after contact is made, a shift occurs in the rate of crossfeed of the wheel with respect to the work from the rapid infeed rate to a rough rate of crossfeedi. e. suitable for rough grinding, and thereafter the rough grinding of the work surface proceeds. In previou conventional machines, the occurrence of this shift in crossfeed rate from rapid to rough is adjusted for a predetermined amount of crossfeed of the Wheel toward the work. Therefore, when the size of successive rough work pieces varies or the rough surface is eccentric, the shift may occur so long after the wheel makes contact with the work as to damage either the Wheel or the workpiece, because the wheel plunges into the work too fast. On the other hand, if the Work piece happens to have a compartively smaller amount of stock to be removed, the shift in crossfeed rate from rapid to rough will occur so long before the wheel makes contact with the Work that considerable loss of time results.

As is well known in the art, a few seconds difference in the time required for grinding a single Work piece results in a great variation in the productive capacity of the machine for a large volume of successive work pieces and, therefore, it can be seen that any time lost in placing the wheel in operative contact with the work makes a great difference in the economy of grinding. It is principally because of variations in the sizes of a succession of rough work pieces that adjustments of infeed rate cannot be made as a practical matter in previously known machines precisely enough to cut down inefficiencies, particularly at the commencement of the rough grinding step.

The present invention provides means in an internal grinding machine for causing the power requirements of the wheel, and, therefore, grinding efiiciency and speed to reach an optimum peak almost immediately upon contact of the wheel with the work regardless of variations in rough work size, and also to maintain the rough grinding rate substantially at such a predetermined peak throughout the rough grinding part of the cycle and, therefore, to cut down the time of operation and to increase the efliciency of the machine. In general, this object is accomplished by making the shift in crossfeed rate depend upon the amount of power required to drive the wheel which, in turn, depends upon the pressure between wheel and work. The point of shifting will, therefore, vary according to requirements for each individual work piece.

In carrying out the above objective, the wheel is applied to the work immediately with as much force and at as high a rate of feed as the wheel and equipment will stand. One result of applying a wheel to a work piece with such great force is that deflections occur in the wheel spindle and also in the work carrier, so that in a conventional machine, grinding a hole at a high rate of rough grinding crossfeed, the line of contact of the wheel surface with the work will be placed out of parallel with the desired work surface due to deflection of either the wheel spindle or the Work carrier, thereby producing a rough or distorted surface, for instance, in the case of a desired cylindrical surface, a tapered surface is produced at the end of rough grinding which, therefore, requires excessive grinding time for finishing to the actual surface desired during the finish grinding which follows. The wheel wears to a tapered shape under such conditions so that an excessive amount must be removed each time the wheel is trued to cylindrical shape.

Accordingly, to compensate for such spindle deflections during the high rate of crossfeed for rough grinding provided in the machine of the invention, provision is made to maintain the work carrier at such an angle with respect to the wheel during rough grinding that the work surface will be substantially parallel to the desired finished surface. The result is that not only is rough grinding time substantially reduced, but the surface produced by such rough grinding is sufliciently accurate so that less than the ordinary amount of finish grinding time is required to complete the grinding operation satisfactorily.

This change in the angle of the work relative to the wheel during rough grinding is accomplished by pivoting either the work carrier or the wheel head, to bring the work surface and the wheel surface into parallelism, i. e. the surface of the work is parallel with the surface of the wheel during rough grinding even though the wheel spindle or work carrier is deflected. This pivoting movement takes place before rough grinding commences. At the end of rough grinding, however, the work carrier or the wheel head are straightenedi. e. moved to bring the work and wheel surfaces back into substantial parallelism with respect to each other, and the remain in this relation during finish grinding when deflection problems are no longer involved because of much lower pressures between wheel and Work. However, in order to straighten the Work carrier with respect to the wheel without marring the work surface, it is desirable first to remove the wheel in a crosswise direction from the work. But because wheel infeed and r traction crosswise is a relatively slow operation and accomplished, for instance, in most machines by the turning of a feed screw, such separation of work and wheel at the end of rough grinding would result in loss of time were it not for additional features of the invention which provide for a rapid separation of the wheel from the work by means independent of the usual feed and retraction means and herein conveniently designated back-oh? and onset mechanism. In the illustrative machine herein, the backoif operation occurs immediately after rough grinding and thereafter the work head is straightened and then the wheel truing opera tion and finally the finish grinding take place with the wheel remaining in the back-off position. This allows the wheel to re-enter the work with the wheel spindle undeflected to begin the finish grinding. No time need be lost by diminishing the feed toward the end of the rough grinding to reduce deflection. After the end of finish grinding, and the wheel and work have been separated and the parts are moving back to their rest or load position, the wheel head is allowed again to move to a forwardly indexed position ready for a subsequent grinding cycle, which position may herein be conveniently designated the onset position of the wheel. In the illustrative machine, therefore, the wheel remains in terms of crossfeed in the onset position, except when it is backed off from the work at the end of rough grinding and held in such back-01f position until finally retracted by the usual crossfeed means from the work after the grinding cycle is complete.

Some of the above features can be embodied Ill separately and to great advantage in internal grinding machines but when combined cooperatively as illustrated in the machine described herein, they result in a machine having much greater grinding efliciency and a much shorter cycle, and therefore a higher rate of production than previous machines.

In the drawings:

Fig. l is a front elevation view of the machine;

Fig. 2 is a top plan view of the machine;

Fig. 3 is a view partly in section showing the crossfeed mechanism;

Fig. 4 is a view partly in section taken along the lines 4--4 of Fig. 3;

Fig. 5 is a detail View of part of a mechanism for controlling fluid pressure valves; being a view from the front of the machine, as seen in Fig. 1 and with a cover plate removed;

Fig. 5a is an end view of part of the mechanism of Fig. i and taken approximately along the lines 5a thereof;

Fig. 6 is a view similar to 5a with the mechanisms in another position;

Fig. 7 is a view similar to Fig. 5 in the mechanisms in still another position;

Fig. 8 is a schematic flow diagram showing the fluid pressure system and its operating and control mechanism for the machine; and

Fig. 9 is a flow chart showing the conditions of the various valves and fluid lines in Fig. 8 for each of the operative steps of the machine.

For convenience, the machine is illustrated and described as arranged for grinding cylindrical holes with a cylindrical wheel, but it will be understood that it can be arranged for grinding tapered holes.

A machine of the chucking type is used as an example, but the work may be supported and rotated by any desired type of work carrier.

General organization The invention is adaptable to machines in which work size is controlled either by a predetermined amount of feed of the wheel. into the work or by means responsive to gauging of the workitself. For convenience, the invention is shown and described in a machine of the type in which the amount of crossieed of the wheel is predetermined in order to size the finished work piece. Such a machine is shown and described in patent to Blood et al., No. 2,011,705, except that the orossfeed mechanism shown and described herein for the grinding wheel is of the general type illustrated in the patent to Blood. No. 2,097,429.

The various motions including relative work and wheel traverse, crossfeed of the wheel relatively into the work, wheel truing, and also the novel operations hereinafter further described are actuated by fluid pressure means controlled by valves. Some of these valves are actuated mechanically in response to traverse table movement as described and illustrated particularly in Figs, 2-5, 10 and 11, in the patent to Blood et al.,

No. 2,011,705, and also in response to wheel feed as described and shown, particularly Figs. 3 and 4, in the patent to Blood, No. 2,097,429. Some of these valves also respond to changes in conditions of pressure and exhaust in the fluid pressure system and one valve responds also to electric power control means.

Referring to Figs. 1 and 2 herein, the machine is organized on the usual base 6 upon which are mounted for relative traverse and crossleed movement with respect to each other an internal grinding wheel 2 and a rotatable work chuck or carrier 3 adapted to rotate a workpiece W (Fig. 3) being ground by the wheel. The work head 4 is mounted to pivot on a traversing table 6 about a point which is established by a pivot 1 connecting the work head 4 and the traversing table 6. The work carrier 3 can, therefore, be traversed toward and away from the wheel 2 and also pivoted or swiveled into different angular relations with the wheel 2 and back again.

The traverse table 6 is moved by a piston 20, Fig. 8, operating in a cylinder 2| suitably attached to the base I. The work carrier 3 is pivoted out of axial parallelism with the wheel 2 by a piston working against a boss 26 attached to the work head 4 and operating in a cylinder 21 attached to the table 6. The work carrier 3 is pivoted back into axial parallelism with the wheel 2 or straightened by another piston 29 working against the boss 26 and operating in a cylinder 30 also attached to the table 6.

The wheel 2 is mounted on driving means, in

this case an electric motor l0 comprising a wheel head 16 on crossfeed mechanism indicated at 9, including a crossfeed table l2 slidably mounted on a bridge I3, so that the wheel 2 can be fed in a crosswise direction normal to its axis of revolution and against the work W.

The crossfeed table I2 is moved to feed the I wheel 2 against the work W, Fig. 3. by the usual feed screw received in a nut 4| attached to the table I2. The feed screw 40 is rotated by a piston 45, Fig. 4, operating in a cylinder 46 attached to the base I. Connected to the piston is a rack 48 moving a pinion 49 loose on a hand wheel shaft 50 and fast with an annular member 51 on which are mounted a pair of ratchet pawls 52 and 53 adapted to engage a circular ratchet 5 5 which is fast on the shaft 50. This shaft 59, in turn, drives the feed screw 40 through gears 55 and 56.

The feed screw 46 is mounted not only for rotation in the bridge I 3 but also for a limited endwise movement for rapid back off and onset of the wheel 2 with respect to the work Wi. e. away from and toward the work during the cycle. For thlis purpose, the right-hand end of the feed screw 40, see Fig.3, is connected to a piston 66 operating in a cylinder 61 attached to the bridge 13. The piston and hence the feed screw 40 and crossfeed table l2 are normally urged by springs 63 to the right into onset position toward the Work against an adjustably positioned set screw 64 which establishes the onset position. Thus, in addition to the usual feed and retraction motion imparted to the wheel by operation of the piston 45 and rotation of the feed screw 40, the wheel 2 may also be quickly backed away from the work to back-off position by endwise movement of the feed'screw imparted by operation of the piston 60 and thereafter allowed to return to an onset position under the force of the springs 63.

The machine also has a wheel dressin or truing tool I 5 carried on the table 6 and which during the machine cycle is operated to true the wheel 2 by fluid pressure mechanism and described in said Blood et al. Patent No. 2,011,705, including a piston l8 and cylinder l9, seen in Fig. 8 herein and returned to inoperative position by a cam l6 in back of the wheel head Ill engaging a cam follower H as the work carrier 3 is returned to operative position with respect to the Wheel 2.

The. machine cycle starts with the machine at rest or load position as illustrated in Fig. 1 in which the workpiece is loadedv in the work car-, rier 3 and with the traverse table 6 at its extreme left-hand position, In this position, the work carrier 3 has been pivoted out of axial parallelism with the grinding wheel 2i. e. from a straightposition in which the axes of rotation of the wheel 2 and work carrier 3 are parallel to a pivoted position in which they are out of parallel, as shown in Fig. 2.

The crossfeed table l2 has been allowed to come into the onset position, but otherwise the crossfeed table I2 is in the retracted position, or to the left, as in Fig. 3 as established by retraction of the piston 45 to the right as shownin Fig. 4.

The wheel 2 is, therefore, in position to enter the work W without touching it during traverse of the table 6 to the right to bring the wheel and the work into relative operative position. When the drive motors 5 and [0 have been energized and the cycle is started, the work carrier 3 feeds rapidly to the right toward the wheel in a traverse in step. Just as the wheel 2 relatively enters the work W, the wheel also moves rapidly crosswise on its table 12 toward and against the work W in a "rapid infeed step, and at the same time an oscillating motion is imparted to the traverse table 6 to move the wheel 2 relatively back and forth across the face of the Work W during grinding. Even after the wheel 2 makes contact with the work, it continues to be ,fed crosswise rapidly into the work until a predetermined optimum rate of power is required by the motor 10 to turn the wheel to grind the work under rough grinding conditions, at which point v means responsive to the absorption by the wheel of said predetermined amount of power are operated to cut down the rate of flow of fluid under pressure against the piston 45, so that the wheel is thereafter fed against the work at a slower rate during the rough grinding step, which rate is adjusted so that substantially the said optimum amount of power is continuously absorbed by the wheel during rough grinding. When the wheel has thus been fed crosswise by a predetermined amount to rough grind the work, the wheel is then backed quickly away from the work during a start out and back off step in which the piston 60 backs off the wheel 2 and crossfeed table I 2 from the work, and at the same time the traverse table 6 stops oscillating and starts to move more slowly out to the left away from the wheel 2 preliminary to a wheel truing and work head straightening step. At this time, in the true and straighten step, the work carrier 3 is straightenend back into axial parallelism with the grinding wheel 2, and the dressing tool [5 is then operated to dress or true the wheel. With the wheel held in back off position, the traverse table 6 then moves the work back to the wheel for a finish grinding operation. The wheel is then fed crosswise into the work at a still slower rate by movement of the piston 45 to commence the finish step, and the traverse table 6 is again oscillated to move the wheel relatively across the face of the work and finish grinding continues until the wheel has been further fed crosswise by a predetermined amount. When the finish grinding operation has been completed, the cross feed piston 65 is reversed and moves to the right and retracts the wheel from the work in the retract and start out step. At the same time, the traverse table 6 moves to the left toward the rest position. The finish grinding operation having taken place with the wheel at the back-off" position, the cross feed table [2 is now allowedto return the wheel to the onset position with the piston 60 against the set screw 64. At the same time the work head 4 and work carrier 3 are again pivoted out of axial parallelism with the wheel 2 ready for a subsequent cycle. When the traverse table 6 has returned to the position of Fig. l, the machine comes to rest and the cycle is finished and ready for a subsequent cycle of operation.

Operating and control mechanism The operating system, best illustrated as a whole in Fig. 8, includes a fluid pressure control valve I for convenience herein designated a front valve, a valve I for convenience designated a rear valve, these valves operating for purposes to be described, and a reversing valve I50 which controls direction of movement of the table 6. These valves are mechanically actuated by the mechanism herein shown in Figs. 4 to '7, inclusive, and as described and illustrated more fully in the patent to Blood et al. No. 2,011,705. This mechanism is responsive partly to the motion of the traverse table 6 and partly to the motion of the crossfeed mechanism 9. The rear valve 120 is also partly operated by fluid under pressure.

The rate of crossfeed of the wheel into the work is partly controlled by a valve I30, for convenience here designated the cross feed valve which is actuated partly mechanically by the crossfeed mechanism 9 and partly by fluid pressure. The feed valve I and its operating mechanism is of the general type shown in Blood Patent 2,097,429, particularly Fig. 4 thereof, but herein some what modified for the purposes of the invention. The crossfeed rate is also controlled by a valve I for convenience called the power pick-up valve which is operated in one direction by a solenoid I42 and in the other by fluid pressure as further described.

A fluid pressure operated delay type valve 160,

conveniently called the swivel onset valve, a

fluid pressure operated delay type valve I'IO, conveniently called the swivel valve and a fluid pressure operated valve I80, conveniently called the "onset valve, also cooperate with the aforementioned valves for operating the fluid pressure system to actuate the traverse table 6, the crossfeed table I2, the dressing tool I5, the work head pivot piston 25, the work head straighten piston 29 and also the back-01f and onset piston 60.

Referring to Figs. 1, 5 and 8, the reversing valve I includes a valve member ISI which to start the cycle can be shifted manually by a lever I on a shaft I55c operatively connected to the valve element l5l, through a yoke I56 which engages a pin 15'! on a second yoke [58 which, in turn engages a pin I59 on a crank 159a fast to the valve member I5l.

This moves the table 6 to the right into the grinding position and thereafter an oscillating motion is imparted to the valve member I5I and, therefore, to the table 6 and work carrier 3 by a pair of resiliently mounted downwardly depend ing reversing dogs 80 and 8i which successively abut and alternately move the arms 82 and 83 of a yoke 84 fast to the reversing yoke I58 as the table oscillates back and forth.

At the end of rough grinding, the reversing dog (H is lifted and rendered inoperative in order to allow the table 6 to move part way to the left for dressing the wheel by mechanism including an arm 86 mounted on a shaft 8! and having a lower arm 88 abutting a pin 89 on another arm 8 99 also mounted on the shaft 87 and urged to the right by a spring QI.

Referring to Fig. 4, mounted on the annular element 5! of the crossfeed mechanism is a cam 58 arranged to engage successively a pair of adjustably mounted set screws 93 and 94 on a rocker arm 95 pivotally mounted on a shaft 95 and connected to a trip arm 9? through a link 98 and a bell crank arm 59. The cam 53 engages the set screw 93 at the end of rough grinding moving the trip arm 9? part way to the left. At this time, referring to Fig. 5, the left hand operative end Sla of the trip arm 97 engages a latch lo pivoted at H and having an arm '12 engaging a notch I3 on a projection 1d of the arm 99. The latch I9 is rocked clockwise releasing its arm 1'2 from the notch 33 and allowing the arm .86 to move counterclockwise around the shaft Bi and. upwardly against the stop dog 8! under the pressure of the spring 9! rendering the dog 81 inoperative. The lower end of the upper arm 50 operatively engages a member ID! in the front valve I09, moving it to the right to slow down the traverse motion of the table 6 for wheel truing as will be further described. When the table 6 completes its partial movement to the left for the truing and workhead straightening operations, a resiliently downwardly depending reversing dog engages an upper portion of the arm 83 again reversing the valve member (5i sending the table 8 back to grinding position and recommencing its oscillating motion. When the table 6 returns to the right to grinding position, a dog it depending from it engages the arm to lower it out of the way so that the oscillating traverse motion may be resumed. The dog 76 is pivotally mounted and arranged so that it can turn counter-clockwise but not clockwise so that it passes without effect over the arm 88 when moving to the left, but engages it when the table 6 moves to the right. The arm 86 is latched downwardly out of position after the truing operation by a pivotally mounted latch H which engages another latch 78. The latter is placed in upward. operative position for engagement by the latch "H as shown in Fig. 6 by engagement between 9. depending dog Hill on the table 5 and a trip member i9! pivotally mounted on a rock arm I92 connected by a link I93 to the latch 18. As the table 6 moves out to the left during the truing operation, the dog I96 engages the trip member lSl, and the latch it assumes the position of Fig. 6 Where it is held by a valve member 2| in the valve I20 which has in the meantime moved to the left and under a surface 79 of the latch 18. Thus when the arm 90 moves back to the left, the latch 'li engages the latch it as shown in Fig. 7, thereby holding the arm 96 and the valve member Illl in left-hand position and the arm 85 down out of the way of the reversing dog 80 and 8i. 7

Grinding continues at a finish feed rate until the cam 58 in the crossfeed mechanism engages the set screw 94 moving the trip arm 97 further to the left. The latter movement causes the end 91a, of arm 91 to engage a latch I92 pivotally mounted behind the latch 7G and having an arm I93 engaging a notch H94 in a boss E95 of an arm I96 pivotally mounted on the shaft 81 behind the arm 98. The arm Hi6 has a pin I91 (seen in Fig. 5a) engaging an arm I98 similar to the arm 88 and integral therewith and with the upper arm 85 on the shaft 8?. When the latch I93 is released by the trip arm ill, the arm I 96 moves to the right again lifting the arm 86, raising the reversing dog SI out of operative position with respect to the arm 83 of the reversing yoke 84,

9. and the table 6 can move out to the left again to rest position after finish grinding.

The elevation of the arm 86 during this latter motion is higher than under the influence of movement of the arm 90 and, therefore, the dog I is also held'out of operative engagement with the reversing arm 83 as the table moves outwardly to the left, allowing the table 6 to continue all the way out to rest position.

The bottom of the arm I93 is operatively attached to the valve member I2I of the rear valve I and as this arm moves to the right, the valve member I2I is also shifted to anextreme right hand position to retract the wheel crosswise as the table 6 moves to rest position; Thearm 86 being left in an upward position when the machine comes to rest, during a subsequent grinding operation when the table 6 traverses to the right toward grinding position, the depending dog I6 engages the arm 85 moving it'downwardly, releasing the latch I8 from the latch 11, allowing the trip member I91 and the rock arm I92 to return to upward position andmoving the'valve member I2I from its right hand position to its center position.

Referring to Fig; 4, the crossfeed valve I is a three position valve. It has'a valve member I3I which has three operative positions designated left, center and right, andwhich operatively abuts against a camv follower member I32 having a suitable roll I33 positioned to ride on a cam 59 on the annular member 51' during a portion of the rotation of the member 5'! under the influence of the movement of the piston 45 to the left. The valve member I3I is normally urged to the left bya spring I34. Its left hand position is shown in Fig. 4 where it remains during rapid infeed and rough grinding- Itscenter position is established by the cam 50 duringflnish grinding and fluid pressure against its'left hand end moves it to its right hand-position for retraction of the wheel. The cam 59 may be adjustedcircumferentially of the annular. member 51 to cut down. the rate of wheel infeedforflnish grinding.

The power pick-up valve l40-controls the shift in crosswise wheel feed rate from a rapid infeed rate to the rough grinding infeed rate. It has a valve member'MI which is moved to the right to open the valve I40 by fluid; under pressure exerted against its left end andto the left by a solenoid I42. The solenoid I 42fis energized by the closing of a normally open relay switch I43 when a relay I44 is energized by current passing through a Wheatstone bridge'rectifler I45 coupled to one side I4Ba of a transformer I46, the other side I4! of which is connected in'series with one of the power lines I48 of the wheel drive motor I0. Thus the valve member I4I being to the right with the valve I40 open, when a predetermined amount of current or power is used by the motor ID to turn the grinding wheel 2 for rough grinding, the relay I44is energized to close the switch I43 and energize the solenoid I42 which moves the valve member I4I to the left to close the valve I40 and cut down fluid flow to the piston 45 and hence the rateof wheel feed.

' Fluid pressure system Referring to Fig.8, fluid under pressure is supplied to the system by a suitably actuated pump 200 drawing fluid from a sump orsupply 20I', the fluid being distributed from-the pump 200 to a supply line 202. Referring also to Fig. 9, when the cycle commences with the machine at rest 10 in the load position, the valve member IOI of the front valve I00 is to the left, and the valve member I2I of the rear valve I20 is to the right as previously described. The valve member I3I of the feed valve I30 is to the extreme right where it has been moved and held by fluid under pressure, as further described. The valve member I4I of the power pick-up valve I40 is to the right and this valve is open. The reversing valve I50 is in the out position with its valve member I5I in the position shown inFig. 8. The valve I member I6I of the swivel-onset valve I has been moved to the right by fluid under pressure, as further described. The valve member III of the swivel valve I has been moved to the left under pressure of the spring I72. The onset valve I has been moved to the left by fluid under pressure as further described.

In this condition of the valves for load position, fluid under pressure from the pump 200 passes from the line 202 through a branch 202a, a manually adjusted throttle valve 205 and across the valve I00 into the branch line 2001) of a line 209, through a line I52, across the valve I50 and thence to the right hand side of the piston 20 through a line I53, holding the traverse table 6 to the left in the position shown in Fig. 1-. Fluid exhausts from the left side of the piston 20, through the line I54, across the valve I50, and through an exhaust line I55, to the sump 20L Fluid under pressure passes from the line 202 and .a branch 202] across the valve I20 into a branch 2 Ilia of a line 2") and to the left hand side of the piston 45 of the cross feed mechanism holding the latter in retracted position. Fluid under pressure also passes from the line 2I0 through a branch 2 I0b to the left side of the valve member I3I of the cross feed valve I30 holding the member I3I in its extreme right hand position against the spring I34. Therefore, the right hand side of the piston 45 is open to exhaust through a line 204, a branch 220aacross the valve I30, and into an exhaust line 220 to the sump 2M. A line 2041!. is also under pressure across the valve I00 from a branch 2020 of the line 202,

thereby charging with pressure a line 2041) across the open valve I40 from a line 204a and through a manual cross feed main throttle valve 206, and also a pair of branch lines 2042 and 2047' through a manual rough rate cross feed throttle valve 201, and a manual finish rate cross feed throttle 200, respectively. The lines 204b, 2041' and 2047' are inoperative in the above valve condition because the valve I30 is closed to them, but they tare charged and ready for a subsequent operaion.

Pressure in the line 2I0a has also passed through a branch 2I0c, a manual throttle valve 2I2, and into the swivel-onset" valve IE0 at the left side of the valvemember I6I, holding the latter to the right. This has allowed fluid under pressure from another branch 2I0d of line 2I0 to pass across the valve I60 to a branch 2 I I a of a line 2II through which it has flowed during the swivel and onset step to the cylinder2'l exerting force on the piston 25 to pivot the work head 4 out of axial parallelism with the grinding wheel v2 as shown by the relative position of the work head .4 in Fig. 2. Pressure in the line 2II has'also entered the left hand side of the valve I40 through a branch 2i lb to move the member I4I to the, right to open the valve: 140. Fluid under pressure in the line'2 I I has also entered the valve I80 to the right of its member through a branch line 2IIc, thus holding the valve member I8I to the left and allowing fluid in the offset and onset cylinder to exhaust through a line 2031) across the valve I80 and through an exhaust line 2030 to the sump 20!, thus allowing the back off and onset piston 00 to remain forward against the set screw 64 with the crossfeed mechanism in onset positioni. e. with the grinding wheel toward the work.

Fluid exhausts from the straighten cylinder 30 through a branch line 203a, a check valve 2 I3, a line 203, a branch line 2036 across the valve I00, and thence into the exhaust line 2030 to the sump 20I. Fluid also exhausts from the truing tool cylinder I9 into the line 203, allowing the piston I8 to remain inoperatively to the right. Fluid exhausts from the left side of the valve member III of the valve I'III through a throttle valve 2I4 and branch line 203e into the line 203, allowing the valve member I'II to remain to the left under pressure of the spring I12, thus closing the valve I10 between the lines 203a and H The traverse in step is initiated by manually moving the reversing valve member I5I counter-clockwise by operation of the lever I55, Fig. l, and the fluid pressure and exhaust conditions are reversed in the lines I53 and I54, pressure in the line I54 moving the table 6 rapidly to the right to traverse it into operative position with respect to the wheel 2 after which it commences oscillating. At the commencement of oscillation of the traverse table 6, fluid under pressure flows from the line 202 to the supply line 209 for the table cylinder 2!, not only from the branch line 2091) but also from a branch line 2090 across the valve I from a supply branch 2026 for' a. more rapid rate of traverse during oscillation of the tool.

When the wheel has relatively entered into operative relation with respect to the work, the rapid in-feed step is started automatically in which the wheel moves rapidly into the work by actuation of the cross feed piston 45. mencing the rapid in-feed step, the valve member I2I of the rear valve I20 is: moved from right to center position by the valve control mechanism previously described. This position of the valve is shown in Fig. 8. The valve I00 remains in its left-hand position also as shown in Fig. 8. Because of the change in the condition of the valve I20 from right to center position in which it is shown in Fig. 8, fluid now exhausts from the'left side of the piston 45 through the line 2 I0, 2I0u, across the valve I20, and into an exhaust line 2I6 to the sump 20L Fluid thus also exhausts from the left side of the valve member I3! of the crossfeed valve I through the line 2I0b, and into the line 2I0 to the sump, thus allowing the valve member I ill to move to its extreme left position as shown in Figs. 4 and 8. When the valve member I3I moved to the left, the line 204f was closed to the exhaust line 204g. The. line 20% being under pressure, as previously described, the fluid now flows from it through the main throttle valve 206, the line 204a, the open power pick-up valve I40, the line 24% and across the crossfeed valve I30 through a branch line- 2040 into the right hand Comside of the piston 45. Fluid also flows to the right side of the piston 45 from the throttle valve 206 across the rough feed throttle valve 201, through the branch line 2042, and across the valve I30 to the branch 204d of the line 204. Thus the piston 45 moves rapidly to the left to feed the wheel crosswise into the work during the rapid infeed step.

As the line 2I0 becomes open to exhaust through the branch 2I0a, the liquid on the left side of the valve member IOI of the swivel-on set valve exhausts through the valve 2I2 and line 2 I00, allowing the valve member ISI to shift to the left. This releases pressure from the pivoting cylinder 21, and from the left side of the valve member I4I of the power pick up valve I40, thus allowing the piston 25 to be moved when the wheel head is later straightened and allowing the valve member I 4! to be moved to the left by the solenoid I42 at the end of rapid infeed of the wheel. The right side of the valve member IOI in the onset valve I is now also open to exhaust through the line 2IIc allowing the member I8I to shift to the right under pressure of the spring I82 and trapping the fluid in the line 20372. The condition for rapid infeed being fully established, the grinding wheel 2 is now feeding rapidly into the work W and continues the rapid rate of crossfeed after making contact with the work, thus very quickly causing a large power requirement from the wheel drive motor I0 as the wheel plunges into the work. The instant this amount of power, as absorbed by the wheel in cutting the Work, reaches a predetermined optimum adjustable amount, current through the transformer elements I 46 and I4"! and bridge I45 energizes the relay I44 sufficiently to close the relay switch I43. This energizes the solenoid I42 which, in turn, immediately shifts the valve element MI in the power pick-up valve I40 to the left cutting off the how of fluid under pressure to the piston 45 from the line 204a to the line 204?). This allows fluid under pressure to the piston 45 to flow only through the throttle valve 201. The latter is adjusted to meter the fluid flow so that the rate of movement of the piston 45 will be at a rough grinding feed rate such that the said predetermined amount of power will continue to be exerted by the drive motor I0 for turning the wheel during rough grinding. Thus the shift from the rapid in-feed rate to the rough feed rate for the grinding wheel 2 depends upon the power requirements for the wheel 2 during rough grinding and not upon a predetermined amount of in-feed of the wheel. This prevents what is known as grinding air which occurs when the shift from rapid in-feed to rough grinding feed is dependent upon the extent of feed of the wheel towards the work and when the amount of work to be ground in a particular work piece is less than that for which the shift from rapid to rough infeed rate is adjusted. It also allows the immediate attainment of a maximum power load on the wheel 2 instead of a gradual build up as occurs when the shift depends upon the extent of wheel feed. Once the power pick-up valve member I4I has been shifted to the left by the solenoid I42, it remains there until returned to the right by fluid pressure in the line 2| ID.

The "rough in-feed rate of the wheel being commenced by the shifting of the power pick-up valve member I4I to the left, the rough grinding step continues with no other change in the condition of the valves in the system until the cam 59 moves the valve member I32 from the left to the center position, at which time also the cam 58 engages the setscrew 9.3 to move the front valve I to the rightas previously described. At the same time, fluid pressure in the line 203 moves the rear'valve I20 from its center position to its left hand position as further described. This condition of the valve commences the start out andback off part of the cycle in which the traverse table 6 commences moving out to the left for the wheel truing operation by the dressing tool I and in which the wheel is backed away from thework by fluid pressure exerted on the back-off piston 00 and in which the work carrier 3 is straightened or pivoted back into axial parallelism with the wheel 2 preparatory to a finish grinding operation. To commence this part of the operation, the reversing valve member I5I is also moved into the position shown in Fig. 8 as previously described to introduce fluid to the right side of the piston 20 to move the table 6 to the left.

In this valve condition for start out and backofi, lines 209i?) from the front valve I00 and 2090 from the rear valve I20 are closed, but line 209a is open to pressure across the valve I00 from a branch 2021) of thepressure line- 202 and through a throttle valve 2I5 which is adjusted to slow the rate of traverse of the table fi to a rate suitable for truing the wheel. The pressure supply line 20471. to the cross feed valve I36 is closed across the front valve I00 from its supply branch 2022), thus bringing the crossfeed motion to a stop. The line 203 is open to pressure from the supply branch 202a. across the valve I00 through a branch 2036. Thus introducing the pressure to the right side of the valve member I2I to move the latter to the left and also supplying pressure to the right side of the dressing tool piston I8 to operate the dressing tool I5,., Pressure in the line 203 also enters the branch 2036 introducing pressure to the left side of the swivel valve member ITII through the throttle valve 2H5, but the throttle valve 2-I4 is adjusted so that the valve member III delays in its shift to the right until pressure from the line 203 has also passed through a check valve 2II and through the line 2032) into the back off cylinder 6| to move the piston 00' and to back the wheel away from the work. Thereafter the fluid under pressure crosses the valve I10 whose member III has completed its delayed movement to the right, and through the branch line 203a into the cylinder 30 to straighten the work carrier .3 and to move it back into axial parallelism with the wheel 2. The truing operation meantime being carried on, the true and straighten step is brought to completion.

The shift in member IZI of valve I20 from center to left hand position does not affect the condition of the fluid pressure system, except for the closing of branch line 2090 to slow the rate of traverse of the table 6 during the truing operation.

At the completion of truing the wheel and straightening the work head 4, the fflnish grinding step commences, in which the traverse table 6 returns to the right to bring the work again into operative position with respect to the wheel as previously described and to cause return of the front valve member IM to the left, the rear valve member I2I remaining to the left. Oscillation of the traverse table 6 recommences as. previously. described, but at a. slower rate,

because the fluid under pressure passes-to the valve I50 only through the branch line 200b, from the supply branch line 202a through the throttle valve 205. The fluid pressure supply line.,204h has now been reopened'to pressure from the supply branch 2020 across the valve I00, and the feed valve member 'I3I having been moved to center position by the cam 59, fluid under pressure now flows to the right side of the feed piston 45 only through the finish rate throttle valve 208 and the supply branch 2047' across the valve I30 to the supply branch 204:2 causing a slower rate of crossfeed for the finish grind.- ing operation. The branch lines 2040 and 20411 are now closed at the valve I30.

The. finish grinding continues until the cam 58 on the annular member 51. of the crossfeed mechanism engages the set screw 90. to cause movement of the. rear valvev member I2I to the right to commence the retract and start ou step. The branch line. 2I0a and the line 2I.0 are now placed under pressure to retract the crossfeed piston 45 to the right and also pressure is exerted in the line 2I0b to move the crossfeed valve member I3I to the extreme right hand position. The branch line 204e is now also. closed to pressure at the valve I30 and thebranch' 204i is open to' exhaust from the right side of the piston 45 across the valve I30 to the exhaust line 220 allowing rapid retraction of. the wheel from the work by movement, of the piston 45. to the right. Pressure in the line 2I0 also flows through the branch 2100 and the throttle valve 2I2 to the left side of the swivel-onset valve member I6I which, after a delay, moves to the right as shown in. the swivel and onset condition in Fig. 9. The traverse table 6 is now moving to the left toward rest. position, andby the time the work and the wheel are separated, the valve member I6! has completed its movement to the right allowing pressure to flow through it from the branch line 2I0d into. the branch line 2| Ia and thence into the line. 2I I.. Pressure in the latter line is exerted against the pivoting piston 25, moving the work head 4. into a position in which the work carrier 3 is pivoted out of axial parallelism with the wheel. 2. Pressure in the line 2 is also exerted through the branch 2I Ic to the right. side of the onset valve member IBI causing the valve I80. to open and to exhaust fluid behind the piston, 60 through the line 203v and into the exhaust line 2030, allowing the piston 60 to move forward against the set screw 6,4, causing the cross fed mechanism to move into onset position preparatory for a subsequent operation. Pressure in the line 2II is also exerted through the line 2I Ib on the left side of the valve member I II, moving the latter to the right and allowing pressure into the line 25 1b for rapid in-feedduring a subsequent cycle when the crossfeed valve member I3I again returns to left hand position. The latter operations occur while the traverse table 6 is moving to restposition, and. whenthe work head 4 has reached the position shown in Fig. 1 the cycle is complete and ready to be repeated, after replacement of the work piece, by manual operation of the reverse valve member I5I by means of the lever I55.

The invention is capable of many modifications. For instance, the pivoting feature by which the angle between work and wheel is changed during the cycle can be embodied either by pivoting the work carrier'as. in the illustrative machine, or by pivoting the. wheel; head.

15 Furthermore, the pivoting feature can be arranged to combine its primary function of moving the work carrier relatively out of axial alignment with the wheel with the back-oif feature in which the wheel is removed quickly from the work after rough grinding while the work is being brought back into axial alignment with the wheel, that is, the pivot point can be so arranged that straightening the work with respect to the wheel will have the effect of backing the wheel away from the work so that the separate back-off and onset mechanism described herein can be eliminated. Furthermore, the pivoting feature may be also adapted to serve the function of wheel feed into the work in combination with the function of the usual crossfeed mechanism. Since rough feeding at the high rates possible under this invention causes spindle and other deflections, it is necessary to retract wheel from work before finish grinding in order to allow the deflections to be relieved. The feature of rapid back-oil and onset means in addition to the usual crossfeed means solves this problem of relief of deflection without loss of time because the amount of retraction required is much less at this stage and eliminates rapid infeed before finishing. The machine is arranged and adjusted so that when the wheel enters the work after truing, its surface will be close to or touching the work surface, ready to start finish grinding without loss of time. If back ofi (retraction after roughing) is procured entirely by the relative straightening motion of the wheel and work supports and without additional back off means such as the piston 60, the work or wheel should be so located with respect to the pivot I that straightening will separate the wheel and work only enough to relieve the deflections and to bring the wheel and work into the desired relation so that when the wheel re-enters the work after truing, no time will be lost in starting the finishing operation.

The pivoting and straightening motions have been described herein as a relative change of angle between work head or support and wheel head or support. These motions may also be described as a change of angle between the wheel head or work head and the path of relative reciprocation between them during grinding.

It will be apparent that while the preferred embodiment is shown as a fluid pressure actuated mechanism, the invention may be embodied in a machine which is entirely mechanically actuated and controlled, or in which actuation and control is electrical or in machines which are actuated and controlled by combinations of these and other systems.

Since the power supplied to the wheel drive motor it is a direct function of the power required to turn the wheel against the work, the power pick up valve M0 is preferably responsive to the wheel drive power supply as illustrated herein. However, it can be seen that the power required to rotate the workpiece carrier ills also proportionate to the amount of power required to drive the wheel during rough grinding, so that, within the scope of this invention, the power pick up valve Mil or other equivalent feed control means could be made responsive to the power supply for rotating the workpiece.

The same machine may be used to grind tapered bores with cylindrical wheels, cylindrical bores with tapered wheels, or tapered bores with tapered wheels. In any case, the work surface and wheel surface are brought into parallelism in their deflected state, and the angle between them is changed to produce parallelism again after the deflection has been largely removed by back-off and reduction in feed rates.

We claim:

1. In an internal grinding machine and in combination, said machine having a grinding wheel, a wheel support and a work support, said supports being movable relative to each other to apply the wheel to grind an internal surface of revolution of a work piece in said work support; infeed means relatively to move the wheel toward and against said workpiece surface, control means for said infeed means operating during the grinding cycle to slow the rate of infeed from a rapid rate to a predetermined rough grinding rate, said control means being arranged to operate automatically when the power required to turn the grinding wheel reaches a predetermined rate, and means automatically to change the angle between said supports by an amount substantially suflicient to compensate for changes in deflections in the supports caused by a change in rate of infeed between thewheel and the work during grinding.

2. In the combination as set forth in claim 1, back ofi means independent of said feed means to back the wheel away from the work by an amount suflicient substantially to relieve said spindle deflections, said back off means operating at a point in the machine cycle prior to said change in angle between said supports.

3. In an internal grinding machine and in combination, said machine having a grinding wheel, a wheel support and a work support, said supports being movable relative to each other to apply the wheel to grind an internal surface of revolution of a work piece in said work support, infeed means relatively to move the wheel toward and against said work piece surface at changing rates of infeed, means automatically to pivot one of said supports away from axial parallelism relative to the other at a predetermined point during the grinding cycle by an amount substantially sufficient to compensate for deflections in the supports during rough grinding, means relatively to back the wheel away from the work after rough grinding by an amount suflicient to relieve at least part of said deflections and means to pivot said support back toward axial parallelism relative to the other prior to reapplication of the wheel to the work for finish grinding.

4. In an internal grinding machine and in combination, said machine having a grinding wheel, a wheel support and a work support, said supports being movable relative to each other to apply the wheel to grind an internal surface of revolution of a work piece in said work support, infeed means relatively to move the wheel against said work piece surface at changeable rates of feed for rough and finish grinding, means automatically to move one of said supports pivotally away from axial parallelism relative to the other at a predetermined point during the grinding cycle by an amount substantially suflicient to compensate for deflections in the supports during rough grinding and means to move said support pivotally back toward axial parallelism relative to the other, said pivoting movement being centered at a point so located with respect to said parts that said deflections are relieved when said parts are pivoted back toward axial parallelism.

5. In an internal grinding machine and in com- 1 71* bination, said maclimediavingagrinding wheel; a wheellsupport; and a=work=support; infeed means" relatively to move the wheel support to "apply-the wheel against 1 an internal surface of awork piece the wheel support, means angula rly to position samsupports relative to each other-:to "compe'nsate for deflections I in saidsupports== causedby a relatively rapid rate of application of the wheeP'to' the work piece,- control means; forsaid infeed meansoperating automatically to slow the rate of infeed' from a rapid rate to" a-=pr'ede'terminediro'ugh grinding rate-whenithe=power re quired to turn the wheel reaches-a predetermined rate, backf offl means: independent of saidf infeed means-operating at a p-redetermined point to back the wheel away from the work sufficiently to reliece said deflections, means to change the angle between said supports by-an amount substantially sufficient to compensate: 'forchangesa in :said: de-

fiections caused by a reduction-of-the rate of-v in-: feed, and means automatically, to reduce. said rate of infeed.

6 In the combination as -set forth in clai'r rr meansiautomaticallyto dress the-wheel at arpredetermined point inthe machinecycle.

w 7". -Inf the combination-- as" set forth in claim 5, means to hold said back ofi-means in backedofi position duringfinish grinding: I

82.In tlie combination-as set-forth inclaim 5, means operating; at;;a.- predetermined point to cause said back off means to move the wheel toward the'work prior to roug'hgrinding.

7 9?;- The method of internal-grinding comprising r'apidlyiee'di-ngthewheelrelatively towardiand against the work, reducing the infeed rate when the power required to move the wheel surface relative to the work surface reaches a predetermined rate for rough grinding, further reducing the infeed rate for finish grinding and changing the angle between the wheel support and the work support to compensate for the resulting reduction in the deflection of the said supports.

10. In the method as set forth in claim 9, the step of angularly positioning said supports during the machine cycle to compensate for deflections in said supports caused by the relatively high rate of infeed during rough grinding.

11. In an internal grinding machine and in combination, said machine having a work piece carrier and a grinding wheel, said carrier and wheel being movable relative to each other to apply the wheel surface to grind an internal surface of revolution of a work piece in said carrier; power driving means for causing relative movement between the grinding wheel surface and the work piece surface, and electric power supply for said driving means, fluid pressure infeed means relatively to move the wheel toward and against the said work piece surface, and control means for said infeed means operating automatically during the grinding cycle to change the rate of infeed, said infeed control means including a relay, a fluid pressure control valve responsive to said relay, and a Wheatstone bridge rectifier to energize said relay, said rectifier being electrically coupled to said power supply and responsive to variations in current therein flowing to said driving means.

12. In an internal grinding machine and in combination, said machine having a work piece carrier and a grinding wheel, said carrier and wheel being movable relative to each other to apply the wheel surface to grind an internal surface of revolution of a work piece in said carrier; power driving means for causing relative moveinfeed-means relativelyto mov J of inf'edbetween-the wheel said driving" means, fiuid' pressure-' -infeed meansi relatively to movethe-- wheel towa'rd and againsti the said' 'work piece surface, and' jcontrol-.meansi for'-- said infeed means "operating: automatically; durin the grinding?cyciextoven i {rat or: infeed, "said infeed -control meansincludinga: relay,- a 'fluid ressure control valve 'responsive a transformer anda wlieatstonei bridge recti'fl'er to energize-sail relay; said reoti fierbeing electrically coupled-througlt saiid tra former to said power supply and resp'onsive too variations-inicurrentitherein flowing to said" r'i ingmeans. 1 2 13. In an internal grinding ma I 4 m combination, said machine-havinga jgri'nding wheel; a wlfeel-supportand a' worie support-, said supports being movable: relative et'o eaclri ether-w: apply th'e 'wlieeI.- to grind an internal surfaceiof revolution of a 4 workpicein -said work suppo;

'the wheel toward urf'ace; cont land against said' --worli-i piec means for said'infee'dmeans I v 'ndithe-work duringi grir'idi'figal pivot -f0;ioi-ie' -of 'said supfi0rt 61 ch'anging its angular relation to. 1 the 1 other L rid mechanismoperativeiy conriected said voted}. support arid responsive to a change in saidrate of infeed thereby pivoting s aic tsupport and "changing tI'ie' angIe-betWeen'said' supports duri'ngf"'grinding1v to oompensate for e-hange's supports causedby 's'aid ch I1 during grinding.

14. In the combination as set forth in claim 13 I means automatically to dress said grinding wheel at a predetermined point in the grinding cycle.

15. In an internal grinding machine and in combination, a work head having a work piece carrier, a wheel head having a spindle and wheel, infeed means to feed the wheel toward and against a work piece in the carrier, said infeed means operating automatically to slow the rate of feed when a predetermined force is reached between the wheel and the work piece, said work head being pivoted for changing its angular relation to the wheel head and pivoting means operatively connected to said work head and responsive to a change in said rate of infeed thereby changing the anglebetween said work head and wheel head during grinding to compensate for changes in deflections in the parts caused by said change in rate of infeed during grinding.-

16. In an internal grinding machine and in combination, a work support, a wheel support having a grinding wheel thereon, said supports being movable relative to each other, means relatively to reciprocate said supports in a predetermined path to move said wheel back and forth across the surface of a work piece during grinding, infeed means relatively to move the wheel toward and against said work piece surface, control means for said infeed means to change the rate of infeed between the wheel and the work during grinding, a pivot for one of said supports for changing its angular relation to said path of reciprocation, and means operatively connected to said pivoted support and responsive to a change in said rate of infeed operating to pivot said support and thereby change its angular relation to said path of reciprocation during grinding to compensate for changes in deflections in the supports caused by said change in rate of infeed during grinding.

17. In an internal grinding machine and in combination, awOrk support, a wheel supporthaving a grinding wheel, a first crossfeed mechanismand a second crossfeed mechanism each having an infeed and a retracted position, each connected to oneof said supports and both arranged, relatively to-move the wheel toward and away from said work piece surface and control mechanism forsaid crossfeed mechanisms operatively arranged to cause one of said crossfeed mechanisms to feed the wheel against the work piece while the other crossfeed mechanism is in itsinfeed position during one part of a grinding cycle; and to feed the wheel against the work during another part of said grinding cycle while the said other crossfeed mechanism is in its retracted position.

;-18.-In an internal grinding machine and in combination; a work support, a wheel support having agrinding wheel, a first crossfeed mechanism connected to one of said supports, a second crossieed mechanism connected to the other of saidsupports, each said mechanism having an inieed anda retracted position and both being operatively arranged relatively to move the wheel toward and away from said work piece surface and control mechanismior said crossfeed mechanisms, operatively arranged to cause one of said crossfeed mechanisms to feed the wheel against the work piece while the other crossfeed mechanism isin its infeed position during one part of a grinding cycle and to feed the wheel against the work during another part of said grinding cycle-while the said other crossfeed mechanism is in its retracted position.

combination, a work supportpa wheel support having a grinding wheel, a crossfeed mechanism relatively to move the wheel toward and against a. work piece in said work support, and control means for said crossieed mechanism, said control means including indexing mechanism providing at least two retracted positionsior said wheel support relative to said work support and means to feed the wheel against the work piece from one of said retracted positions during one part of a grinding cycle and to feed the wheel against the work from another said retracted position during another part of said grinding cycle.

MARTIN L. KUNIHOLM. JOHN KLAR.

REFERENCES CITED The following references are of record in'the file of this patent:

UNITED STATES PATENTS Number Name Date 1,845,172 Morey et a1. Feb. 16, 1932 1,949,552 Taylor et a1 Mar. 6, 1934 1,996,467 Ernst Apr. 2, 1935 2,127,856 Blood Aug. 23, 1938 2,156,970 Burns May 2, 1939 2,367,069 Styherg Jan. 9, 1945 FOREIGN PATENTS Number Country Date 391,479 Great Britain Apr. 20, 1933 669,887 France Nov 21.- 1929 

